2007 Mercedes Benz SL500 Brake Rotors

I am considering buying a 07 Merc Benz SL500 and when I got the CarFax report, it indicated that the front brake pads were replaced at 16,000 miles. That seems unusally low mileage to replace brake pads. When I was examining the wheels I ran my finger across the front rotors and although they were smooth, I noticed that they were a bit wavey. They seem to have ripples across them - on both the right and left front wheels. I looked at rotors on other cars on the lot and did not observe any with these 'ripples'. Is that representative of a problem? Should the rotors be replaced? Any insight you can offer is appreciated. Thanks